1. Field of the Invention
The present invention relates to an air filter unit having the shape of a tube comprising a top plate, having a planar surface distal to the interior of the air filter unit and an air inlet leading into the interior of the tube, whereby the top plate includes fasteners for removably attaching said air filter unit to a wall so that the air inlet of the top plate is concentrically disposed in relation to an opening in said wall, and a sealing ring of a resilient material surrounding the air inlet in the top plate.
2. Description of the Related Art
Air filter units of the above mentioned type have often a double-walled tube with a particulate filter material, especially gas-phase filter media, such as activated carbon, zeolite or porous impregnated aluminium, disposed in the space between walls of the tube. Several of such air filter unit are normally attached to a vertical wall with the longitudinal axis of the tube extending perpendicular to the vertical wall. The function of the sealing ring surrounding the air inlet in the top plate of the air filter unit is to seal the connection between the top plate and the vertical wall. This is done by ensuring that the sealing ring is slightly compressed by the connection of the fastener on the top plate in fastening openings in the vertical wall. When the air filter units are in use, the force of gravity of the unit creates moment forces acting on the sealing ring so that the lower side of the ring is subjected to an additional compressive force component whereas the upper side of the sealing ring is subjected to a tractive force component. This can lead to a leakage of polluted air through gaps between the upper part of the sealing ring and the vertical wall. There is also a risk for excessive wear of the sealing ring making frequent changes of used sealing rings necessary in order to ensure air tightness of the connection between the top plate and the vertical wall.
The objective of the present invention is to significantly reduce said risk for leakage and said wear of such sealing rings by eliminating the influence of the moment forces on the sealing rings.